This invention relates to an exhaust cleaning system for a mrine  marine propulsion engine and particularly to a catalytic exhaust system for such an engine.
In watercraft it is well known that the exhaust gases from the powering internal combustion engine are silenced and cooled by an exhaust system which may include a water jacket that surrounds at least a part of the exhaust system and/or by the discharge of liquid coolant into the exhaust gases for discharge back into the body of water in which the watercraft is operating along with the exhaust gases. The exhaust gas discharge is either disposed below the water level or in proximity to it. Although this type of exhaust system is quite advantageous, there are some disadvantages with it and certain problems which may arise.
For example, it is desirable to provide a catalyzer in the exhaust system so as to insure against the emission of unwanted exhaust gas constituents either into the atmosphere or into the body of water in which the watercraft is operating. Catalyzers are particularly useful in conjunction with two cycle engines wherein there may be lubricating oil mixed with the exhaust gases. The catalyzer can render the lubricating oil relatively harmless to the amorphous in addition to treating the exhaust gases themselves.
However, most catalyzers operate with ceramic type beds and if any water strikes the catalyzer bed, the bed can shatter or become damaged. This is particularly true because of the high temperature at which the catalyzer bed must be at to be operative. These problems are particularly acute with certain types of watercraft which, by their sporting nature, may be capsized and easily righted. During such capsizing operation, water can enter the exhaust system and when the watercraft is again righted, the water can flow back to the catalyzer and cause it damage, as aforenoted.
FIG. 1 of the drawings shows a small watercraft of the type with which the problem aforenoted is particularly relevant, with the watercraft being identified generally by the reference numeral 11. The watercraft 11 includes a hull 12 having a rearwardly positioned seat 13 on which one or more riders may sit in straddle, tandem fashion. A watercraft control, such as a handle bar assembly 14, is positioned forwardly of the seat 13 for controlling the steering of the watercraft and the speed.
The watercraft hull 12 defines an engine compartment that is positioned forwardly of the seat 13 and which contains an internal combustion engine 14 of any known type. For example, the engine 14 may be a two cylinder in-line engine operating on the two stroke principal. The engine 14 has a drive shaft that coupled to an impeller shaft of a jet propulsion unit, indicated generally by the reference numeral 15 and positioned in a tunnel 16 at the rear underside of the hull 12 for powering the watercraft 11 in a known manner.
Conventionally, the engine 14 is provided with an exhaust system which transfers the exhaust gases from the exhaust port to an exhaust discharge and a portion of this exhaust system constructed in accordance with a prior art type of construction is shown in FIG. 2. As may be seen in this figure, the engine 14 has a pair of exhaust ports 17 that discharge into a combined exhaust manifold and expansion chamber 18. An exhaust elbow, indicated generally by the reference numeral 19 delivers these exhaust gases to a further expansion chamber device, indicated generally by the reference numeral 21. It should be noted that the exhaust manifold 18, exhaust elbow 19 and expansion chamber device all have a double walled construction and form respective cooling jackets 22, 23 and 24 each of which receive coolant from the engine 14 in a well known manner. The coolant may be delivered to the cooling jackets 22, 23 and 24 by independent conduits or the coolant may be delivered to one or both of the cooling jackets 22 and 23 in series or parallel fashion from the engine cooling jacket and then delivered to the cooling jacket 24 of the expansion chamber 21.
This coolant from the cooling jackets 22, 23 and 24 is normally discharged back into the exhaust gases that flow from the exhaust port 17 and as may be seen in FIG. 2, the expansion chamber 21 has an inner shell 25 that has a discharge opening 26 that communicates with an outlet pipe 27 but which passes through the cooling jacket 24 so that the engine coolant will be mixed with the exhaust gases as they pass through the exhaust outlet 27. A flexible conduit 28 extends from the exhaust outlet 27 rearwardly as will be described in conjunction with FIG. 1. The cooling jackets 22, 23 and 24 effectively cool the exhaust gases and also insure that the manifold 18, elbow 19 and expansion chamber 21, which are all positioned within the hull 12, will not be overheated.
Referring now again to FIG. 1, it should be seen that the flexible exhaust conduit 28 extends to a water trap device 29 positioned at the rear portion of the hull. The water trap device 29 has an outlet portion 31 that extends to the tunnel 16 so as to deliver the exhaust gases and entrained coolant back to the atmosphere and body of water in which the watercraft is operating.
The type of watercraft 11 is very sporting in nature and can be easily capsized and righted. The water trap device 29 insures that water which may enter the exhaust outlet 31 will not pass back to the exhaust port 17 and interiorly to the engine. However, since coolant from the engine is discharged into the flexible conduit 28, such inversion and righting can cause water from the engine coolant jacket to flow backwardly into the expansion chamber 21, elbow 19 and exhaust manifold 18 and thus possibly enter the engine.
It is desirable to provide a catalyzer, as aforenoted, for treating the exhaust gases and with the aforedescribed construction, water from the cooling jackets 22, 23 and 24 may easily impinge upon the catalyst and damage it.
It, therefore, a principal object to this invention to provide an improved exhaust system for a watercraft wherein a catalyzer may be employed and the catalyzer will be protected from possible damage from the coolant present in the exhaust system and/or water from the body of water in which the watercraft is operating.
It is a further object of this invention to provide an improved catalytic exhaust cleaning system for a marine propulsion engine.
It is a yet further object of this invention to provide an improved exhaust cleaning system for an engine that embodies a catalyzer and an effective device for insuring that the exhaust system may be partially cooled by the engine coolant but this engine coolant cannot come into contact with the catalyzer.
This invention is adapted to be embodied in a an exhaust system for a watercraft that is comprised of a hull containing an internal combustion engine and having at least one exhaust port. The exhaust system is comprised of an exhaust conduit having an inlet end communicating with the exhaust port for receiving exhaust gases therefrom and an outlet end for discharging the exhaust gases to the atmosphere in proximity to the body of water in which the watercraft is operating in at least some conditions of the watercraft. The exhaust conduit includes means defining an expansion chamber and a tube containing a catalyzer bed communicating at one end with the expansion chamber and through which the exhaust gases must pass. Means are provided for precluding water in the exhaust conduit from entering the tube end and impinging on the catalyzer bed.